Packaging laminate with excellent sealing and barrier properties and also packaging container manufactured from the packaging laminate

ABSTRACT

Packaging laminate with excellent sealing and barrier properties comprising a skeletal layer (11) of plastic and filler mixed in the plastic and a barrier layer (12) of plastic of the same type as the plastic in the skeletal layer in a mixture with plastic of another type than the plastic in the skeletal layer, placed against one side of the skeletal layer. 
     In order to improve the sealing properties of the packaging laminate the barrier layer (12) has been provided with electrically conducting material finely distributed in the barrier layer, preferably soot (carbon black) with the aid of which the packaging laminate can be sealed by means of inductive heating (IH) and dielectric sealing.

This application is a continuation of application Ser. No. 08/042,400,filed Apr. 2, 1993, which is a divisional of application Ser. No.07/875,834, filed Apr. 28, 1992.

BACKGROUND OF THE INVENTION

The present invention concerns a flexible packaging laminate in sheet orstrip form with excellent sealing and barrier properties, with thispackaging laminate having a skeletal layer of plastic and filler mixedin the plastic and also a barrier layer of plastic of the same type asthe plastic in the skeletal layer in a mixture with plastic of anothertype than the plastic in the skeletal layer, placed against one side ofthe skeletal layer. The invention in addition concerns packagingcontainers manufactured from the packaging laminate through foldforming, thermo-forming or another mechanical shaping process.

Within packaging technology what are called aseptic packagings are oftenused for packaging and transporting products of a type sensitive tooxygen and/or light. This may apply to liquid foodstuffs such as juice,wine, edible oil and medical/pharmaceutical/biological preparationswhich would otherwise easily be damaged or deteriorate already aftervery short exposure to oxygen and/or light. Aseptic packagings are alsoused for other products such as milk in order to give the packagedproduct an extended shelf life so that it can be kept with maintainedfreshness qualities for very long periods of time without the need forrefrigerated storage.

The requirement that is set for aseptic packagings is that they must beoxygen-tight/lightproof and in addition bacteria-tight in order to givethe best possible protection to the packaged product. Furtherrequirements for the packaging are that it must be form stable andmechanically strong in order to be able to withstand external stressesto which the packaging is exposed during normal transport and handling.It is naturally an advantage if the packaging is in addition easy tomanufacture and after use easy to destroy or to be handled in anothermanner with fulfilment of current environmental protection requirements.

A large group of known aseptic packagings is manufactured from alaminated material comprising on the one hand a strengthening skeletallayer of paper or cardboard, on the other hand a barrier layer ofaluminium (Al foil), which gives the packaging the desiredimpermeability properties, applied to one side of the skeletal layer,and also further coatings of plastic (usually polythene) to make thematerial easy to seal through what is known as heat sealing.

From the known packaging material aseptic packagings of disposablecharacter are manufactured, most frequently with the aid of modernrational packaging machines of the type which, either from a strip orfrom a prefabricated substance of the material, both forms, fills andcloses the packagings on a large industrial scale with a high rate ofproduction. Well known examples of aseptic packagings of this type areTetra Brik (reg. trade mark) and Tetra Rex (reg. trade mark).

A packaging of the type Tetra Brik (reg. trade mark) is manufacturedfrom a strip through the strip first being shaped to a tube through thetwo longitudinal sides of the strip being joined to each other in alongitudinal overlap joint. The tube is filled with the contents inquestion and divided into closed cushion-shaped packaging units throughrepeated transverse sealings of tube zones across the longitudinaldirection of the tube below the filling level of the tube. The packagingunits are separated from each other through cuts in the transversesealing zones and given the desired geometric, usually parallepipedshaped final form in a concluding shaping operation during which thedouble-walled triangular corner flaps of the packagings are foldedagainst and sealed to an adjacent side of the packaging.

The known packaging material has several serious disadvantages which toa great extent and in certain cases can be wholly ascribed to the Alfoil used as a barrier layer, which owing to its low elasticity oftenbreaks in particularly stressed areas of the material during manufactureof the packaging and thereby causes deterioration in the hermeticproperty of the finished packaging. An Al foil is in addition expensiveto produce and therefore contributes markedly to giving the packaginghigh material costs. The known packaging material also has disadvantagesowing to the absorbent layer of paper or cardboard which quickly losesits mechanical strength properties and makes the packaging limp andunmanageable when it is exposed to liquids and moisture. The layer ofpaper or cardboard must therefore be made relatively thick in order togive the packaging the necessary rigidity of form and stability of form,which contributes to increasing the material stress and therewith therisk of formation of cracks in the Al foil during manufacture of thepackaging.

Within packaging technology it has therefore always been an objective tofind alternative packaging materials which neither use a fibre layer norAl foil and which therefore are in practice completely freed fromdrawbacks of the type inherent in the known paper or cardboard basedpackaging materials.

Such an alternative packaging material which at least partly avoids theproblems mentioned here is described for example in EP-A-O 353 991. Thisknown material has a strengthening skeletal layer of plastic and fillermixed in the plastic and has proved to be less costly and less moisturesensitive than the paper or cardboard based material. A similarpackaging material is also described in EP-A-O 353 496.

A packaging material consisting only of plastic and filler mixed in theplastic, as described in both these European patent applications,nevertheless lacks the necessary hermetic properties against both oxygenand light and must therefore be supplemented with at least one furtherlayer of a material with the desired hermetic properties in order to beable to be used in aseptic packagings as intended. The only example ofsuch a supplementary layer that is mentioned in both these patentapplications is, however, the already discussed expensive Al foil whichis prone to cracking.

The Swedish patent no. 468,635 (Swedish patent application no. 9100057-0which corresponds to U.S. patent application Ser. No. 818,156) describesa packaging material which, like the two last mentioned packagingmaterials described above, has a strengthening skeletal layer of plasticand filler mixed in the plastic but which, instead of an Al foil, usesan oxygen barrier layer consisting of plastic of the same type as theplastic in the skeletal layer in a mixture with plastic of a differenttype from the plastic in the skeletal layer. As a particularly preferredtype the Swedish patent no. 468,635 (Swedish patent application no.9100057-0) describes a packaging material in which the plastic in theskeletal layer is to consist of a propylene homopolymer with a meltingindex of less than 1 according to ASTM (2.16 kg; 230° C.) or anethylene/propylene copolymer with a melting index between 0.5 and 5according to ASTM (2.16 kg; 230° C.) and an ethylene/vinyl alcoholcopolymer.

This last described packaging material can, however, be further improvedand the object of the present invention is therefore to give indicationsof how such improvements can be effected.

SUMMARY OF THE INVENTION

The aim is achieved according to the invention through the fact that apackaging laminate of the type described in the introduction is giventhe characteristic that the barrier layer also contains an electricallyconductive material in fine particle form.

Through complementing the packaging laminate's barrier layer withfine-particle electrically conductive material the packaging materialaccording to the invention is given excellent sealing properties, whichamong other things has the effect that it can be sealed with the use ofsealing techniques of such as inductive heating (IH) and dielectricsealing. While a heat sealing of the known laminate withoutfine-particle electrically conductive material sets out to apply theheat necessary for fusion of the laminate's facing layers of plasticfrom outside the laminate the electrically conductive material in thelaminate according to the invention makes it possible to generate bymeans of inductive or dielectric heating the same amount of heat in situin the laminate, which has the effect that the seals can be effectedmuch faster than previously.

The choice of fine-particle electrically conductive material is notcritical according to the invention, but in principle practically anyknown electrically conductive material in this field can be used.Particular advantages are gained, however, if the electricallyconductive material consists of carbon which also makes the packagingmaterial in practice completely impenetrable to light.

The fine-particle electrically conductive carbon material can consistfor example of soot (carbon black) either alone or in combination withother fine-particle carbon, e.g. graphite. Preferably it consists of amixture of soot (carbon black) and graphite since a barrier layercontaining both soot and graphite has proved to be less brittle and moremalleable and easier to shape than a barrier layer containing only soot(carbon black) as fine-particle electrically conductive material. If thebarrier layer only contains soot (carbon black) the amount of soot(carbon black) should be between 10 and 15, preferably 12% weight, sincesoot in quantities of over 15% weight makes the barrier layer brittleand difficult to shape, while soot (carbon black) in quantities of under10% certainly makes the barrier layer malleable and easily shaped but atthe cost of a deterioration in electrical conductivity capacity. If onthe other hand the barrier layer contains both soot (carbon black) andgraphite the amount of soot (carbon black) can be as little as c. 5%without any risk of deterioration in electrical conductivity capacity ifthe graphite at the same time is c. 15-25, preferably c. 20% weight.

According to a preferred embodiment of the invention the packaginglaminate has an external sealing layer of plastic of the same type asthe plastic in the skeletal layer, i.e. either a propylene homopolymerwith a melting index of under 1 according to ASTM (2.16 kg; 230° C.) oran ethylene/propylene copolymer with a melting index of between 0.5 and5 according to ASTM (2.16 kg; 230° C.), applied to the barrier layer.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described in greater detail below with particularreference to the enclosed drawing which shows schematically a crosssection of a packaging material according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The packaging material according to the invention which is shown in thedrawing has been given the general reference designation 10. Thepackaging laminate 10 comprises a strengthening skeletal layer 11 and abarrier layer 12 applied to one side of the skeletal layer(corresponding to the inside of the aseptic packaging produced) givingthe packaging laminate excellent sealing properties and hermeticproperties against both oxygen and light. The laminate 10 in thepreferred embodiment shown has in addition an outer layer 13 applied tothe barrier layer 12 and serving on the one hand to protect the barrierlayer 12 of the laminate against direct contact with the sterilecontents of the aseptic packaging and on the other hand to facilitateheat sealing of the laminate during manufacture of the packaging.

The skeletal layer 11, the barrier layer 12 and the outer sealing layer13 can be manufactured as separate films, each on its own, which aresubsequently joined to each other with the aid of one or moreintermediate binding agents to form the finished laminate 10.Preferably, however, the laminate 10 is manufactured by co-extrusionduring which the layers are extruded simultaneously by a method which isin itself well known and joined directly to each other through fusionwith the use of heat from the extrusion.

The strengthening skeletal layer 11 consists as previously mentioned ofplastic and filler mixed in the plastic, with the plastic in theskeletal layer consisting for example of a propylene homopolymer with amelting index of under 1 according to ASTM (2.16 kg; 230° C.) or anethylene/propylene copolymer with a melting index of between 0.5 and 5according to ASTM (2.16 kg; 230° C.). The amount of filler in theskeletal layer can vary within wide limits and is in general situatedbetween 50 and 80%, reckoned by the weight of the skeletal layer. Thepreferred amount of filler is c. 65%. The type of filler can also varyand in itself does not constitute a critical part of the invention. Inpractice any known filler in that field can be used according to theinvention, even if chalk, clay (china clay), talc and mica each on itsown or in any desired mutual combination with each other form examplesof particularly preferred fillers. The most preferred filler is,however, chalk.

The barrier layer 12 consists as previously mentioned of a mixture ofplastic and fine-particle electrically conductive material mixed in theplastic. The mixture of plastic consists partly of a plastic of the sametype and partly a plastic of a different type from the plastic in theskeletal layer 11. The plastic of the same type as the plastic in theskeletal layer can thus be a propylene homopolymer with a melting indexof under 1 according to ASTM (2.16 kg; 230° ) or an ethylene/propylenecopolymer with a melting index of between 0.5 and 5 according to ASTM(2.16 kg; 230° ). The plastic of a different type from the plastic inthe skeletal layer 11 must be a plastic with good oxygen-tightproperties. Examples of plastic of this type are an ethylene/vinylalcohol copolymer (EVOH), polyvinylidine chloride and polyamide, amongwhich the ethylene/vinyl alcohol copolymer (EVOH) is the most preferred.The fine-particle electrically conductive material in the skeletal layeris preferably a carbon material such as soot (carbon black) either aloneor in combination with graphite.

The amount of plastic of the same type as the plastic in the skeletallayer 11, e.g. ethylene/propylene copolymer with a melting index ofbetween 0.5 and 5 according to ASTM (2.16; 230° C.), can vary between 20and 60% weight, while the amount of plastic of a different type from theplastic in the skeletal layer 11, e.g. ethylene/vinyl alcohol copolymer(EVOH), can vary between 40 and 80% weight. The amount of fine-particleelectrically conductive material which must be used in the barrier layer12 can vary depending on the special choice of fine-particle material.If the electrically conductive material for example consists of soot(carbon black) the amount must be between 10 and 15, preferably 12%weight, while if the electrically conductive material consists of amixture of soot (carbon black) and graphite the relative proportions ofthese two carbon materials must be between 5 and 10, preferably c. 6%weight and between 15 and 25, preferably c. 20% weight graphiterespectively.

The outer sealing layer 13 consists according to the invention of aplastic of the same type as the plastic in the skeletal layer 11 and canthus for example be a propylene homopolymer with a melting index ofunder 1 according to ASTM (2.16 kg; 230° C.) or an ethylene/propylenecopolymer with a melting index of between 0.5 and 5 according to ASTM(2.16 kg; 230° C.).

A particularly preferred embodiment of the invention thus has thefollowing composition of the layers of material in the packaginglaminate 10: the skeletal layer 11 consists of c. 35% weight of anethylene/propylene copolymer with a melting index of between 0.5 and 5according to ASTM (2.16 kg; 230° C.) and c.65% weight filler (preferablychalk); the barrier layer consists of a mixture of 34% weightethylene/propylene copolymer with a melting index of between 0.5 and 5according to ASTM (2.16 kg; 230° C), 40% weight ethylene/vinyl alcoholcopolymer (EVOH), c. 6% weight soot (carbon black) and c. 20% weightgraphite; and the outer sealing layer 13 consists of anethylene/propylene copolymer with a melting index of between 0.5 and 5according to ASTM (2.16 kg; 230° C.).

From a packaging laminate 10 what is known as aseptic packagings aremanufactured with excellent sealing and barrier properties(oxygen-tightness, light-proof property etc.) either through foldforming, thermo-forming or other mechanical form processing of thelaminate. For example from a strip of the packaging laminate packagingsare manufactured, as previously described, through the strip first beingshaped to a tube through the two longitudinal edges of the strip beingjoined to each other in a longitudinal sealing joint. The tube is filledwith the contents in question and divided into closed cushion shapedpackaging units through repeated transverse sealings of the tube belowthe level of contents of the tube. The packaging units are separatedfrom each other through cuts in the transverse seals and are then giventhe desired geometric final form, e.g. that of a parallellepiped,through a final shaping operation during which the double-walltriangular corner flaps of the packagings are folded against and sealedto an adjacent side of the packaging.

A packaging laminate according to the present invention thus solves in asimple and effective manner the previously described problems which areconnected with known paper or cardboard based packaging laminates, atthe same time as it offers valuable advantages in comparison with knownnon-fibre based packaging materials of the type described in for examplethe two European patent applications mentioned or the Swedish patent no.468,635 (Swedish patent application no. 9100057-0). In its mostpreferred embodiment the packaging material is in addition a valuablematerial from the environmental standpoint since all layers forming partof the laminate consist wholly or mainly of one and the same plasticwhich is easy to recover with already existing recovery technology.

I claim:
 1. The process for the manufacture of an aseptic packagingcontainer comprising:making a flexible packaging laminate having askeletal layer with an inner side and an outer side and a barrier layeron the inner side of the skeletal layer, said skeletal layer comprisinga mixture of plastic and filler wherein the amount of filler in theskeletal layer is in the range of 50 to 80% by weight of the skeletallayer, and said barrier layer comprising a mixture of plastic of thesame type as the plastic in the skeletal layer, plastic of a differenttype from the plastic in the skeletal layer with said different type ofplastic providing oxygen impermeability to the barrier layer, and anelectrically conductive material in a fine particle form which allowsthe laminate to be heat sealable by inductive heating or dielectricsealing, and mechanically forming and heat sealing by inductive heatingor dielectric sealing the flexible packaging laminate into a container.2. The process of claim 1, wherein the flexible packaging laminateincludes an inner layer adjacent to the barrier layer such that thebarrier layer is between the skeletal layer and the inner layer, saidinner layer comprising plastic of the same type used in the skeletallayer.
 3. The process of claim 2, wherein the mechanically forming stepincludes fold forming or thermo-forming.
 4. The process of claim 1,wherein the electrically conductive material is homogeneouslydistributed throughout the barrier layer.
 5. The process of claim 1,wherein the electrically conductive material consists of carbon black.6. The process of claim 1, wherein the electrically conductive materialconsists of a mixture of carbon black and graphite.
 7. The process ofclaim 1, wherein the filler is chalk, clay, talc, mica or a combinationthereof.
 8. The process of claim 1, wherein the different type ofplastic providing oxygen impermeability to the barrier layer is selectedfrom the group consisting of ethylene/vinylalcohol copolymer,polyvinylidine chloride and polyamide.